The present invention relates generally to a solid state lighting device or source of the general purpose type. In particular, the invention relates to such a device which comprises a component system incorporating light emitting diodes (LEDs) in order to simulate general purpose incandescent lighting devices.
The present invention further concerns lighting fixtures that incorporate the aforementioned component system in either a single sided or double sided (opposed) configuration.
General purpose LED lighting devices are used primarily in residential and commercial office settings. LED light sources, as well as compact fluorescent (CFL) and linear fluorescent light sources, are generally recognized as the likely replacements for incandescent lighting due to regulatory phase-out of the latter in the years ahead.
Incandescent lighting remains the most popular general purpose lighting technology due to its low initial purchase price and the high quality of its light output. Incandescent bulbs sell for pennies and they provide a diffuse source of broad spectrum illumination that renders colors accurately. In addition, they are capable of task-type lighting at higher power settings, yet can be dimmed down to create very “warm” effect-type lighting at lower power settings. Incandescent lighting remains popular despite the high cost of ownership due to low efficiency and short product life span, especially when the lighting is cycled on and off frequently.
Fluorescent lighting technology is the most popular alternative to incandescent lighting due to a reasonably low initial purchase price, high efficiency, highly diffuse light output and at least the perception of long bulb life. As with incandescent sources, however, life span is greatly reduced when the bulbs are frequently cycled on and off. Fluorescent lighting also suffers from what is generally considered an unnatural quality of light output. Also, dimming a fluorescent product is problematic in that only certain types can be dimmed and then only over a narrow output range. Further, fluorescent products are not capable of spectrally “warming up” at lower power input levels and may even “cool down”, creating an even more unnatural effect. In addition, toxic materials, e.g. mercury, employed in the manufacture of the fluorescent devices require a special disposal process that is often ignored, leading to environmental damage.
LED lighting technology offers the promise of high efficiency, long life and benign environmental impact. Increasingly, the technology is providing high quality spectral output with good color rendering ability. However, the current state of the art has a number of major shortcomings. For example, LEDs are directional light emitters. The high degree of secondary diffusion required to create “soft”, diffuse lighting effects can greatly reduce the overall efficiency of an LED lighting fixture. LEDs also produce very stable spectral output with respect to input power. While this is beneficial for a number of technical applications, the LEDs cannot be dimmed to produce the warmer light output that many consumers prefer for general lighting. Lastly, LEDs can only dissipate waste heat through the process of thermal conduction. Unfortunately, most lighting fixtures have been designed for incandescent light sources where radiation is the primary mode of waste heat dissipation. Resultantly, the life span of LEDs in a conventional lighting device can be reduced greatly because of this mismatch in thermal dissipation modes.